Currently, there has been used a virtualization technique for causing at least one virtual information processing apparatus (sometimes referred to as virtual machine(s) or logical domain(s)) to be implemented on a physical information processing apparatus. Such an information processing apparatus using the virtualization technique executes, for example, software (sometimes referred to as a hypervisor) for controlling logical domains. The hypervisor allocates resources, such as a CPU (Central Processing Unit) and a RAM (Random Access Memory), to the logical domains. On each logical domain, an operating system (OS) is executed. The OS on each logical domain manages the resources allocated by the hypervisor, and controls execution of application programs.
The OS on each logical domain sometimes gets clock access e.g. for acquiring the time of day or performing time-of-day setting. In doing this, it is also possible to convert the current time of day recognized by a logical domain to one which is different from the time of day by a clock device provided in the information processing apparatus (virtualize the clock device). For example, there has been proposed a time-of-day clock control method in which a time-of-day clock offset is held in an actual computer that implements a virtual computer, and a virtual time-of-day clock is realized on the virtual computer using the time of day by an actual time-of-day clock provided in the actual computer and the held time-of-day clock offset (see e.g. Japanese Laid-open Patent Publication No. 04-40552).
By the way, if the number of logical domains implemented on an information processing apparatus increases, this may undesirably increase the frequency of access to a clock device provided in the information processing apparatus. Therefore, the concentration of access causes problems of increased load on the clock device and congestion of a bus to which the clock device is connected, resulting in reduced response speed. On the other hand, even if the number of clock devices provided in the information processing apparatus is merely increased, this brings about a problem of how to ensure consistency in the time of day when a time of day deviation occurs between the clock devices.